ReadyNAS 628 stuck at "NETGEAR Storage Welcome" during 6.9.0 update

So far, ReadyCLOUD reports 628 is offline, and RAIDar also only discovers the Ultra 6 Plus, not the 628, which is connected to the same switch as the U6P and a Mac mini used for access. Forced shutdowns and reboots using the power button on either the front or rear with either the eight data drives in place or a single blank drive returns to the same "NETGEAR Storage Welcome" message without booting.

The 628 had exactly the same behavior and issue a few months ago when the 628 was upgraded from 6.7.4 to 6.8.0. (The 6.8.1 upgrade was routinely successful.) Restarting after a four month shutdown, the 628 finally spontaneously and "auto-magically" finished the firmware update to 6.8.0 and resumed normal operation until the 6.9.0 upgrade attempt. During each major version upgrade (6.8.0 and 6.9.0), the firmware update seems to take much longer than usual before the 628 becomes disconnected from the network during the update progress (e.g., much longer than the 6.7.X and 6.8.1 updates).

At the moment, I have removed and labeled the eight data drives in the 628 and replaced them with one blank drive, and since that hasn't done anything, the 628 is turned off.